1. Field of the Invention
The present invention relates to optical measuring instruments. More particularly, this invention pertains to apparatus for the fine adjustment of a sextant.
2. Description of the Prior Art
In measuring angles by means of a sextant, the alhidade is first roughly adjusted while a drum screw for fine adjustment is disengaged until the object of measurement (e.g. a star) comes approximately into alignment with the line of the horizon. The drum screw is then moved into the limbus toothing and the fine adjustment made by rotating a measuring drum with scale seated on the axis of the drum screw until, for example, the edge of the star reflected into the horizon comes precisely into alignment with the line of the horizon. Before fine-adjustment of the drum screw begins, however, the sextant must be "put down" to determine the zero position on the scale of the measuring drum with engaged drum screw. That is, the user must note (or remember) the degree deviation on the scale of the measuring drum at such moment to be able to carry out a precise positional determination after making the measurement.